Every video picture's viewing dimensions can be represented by a ratio of the picture's width to the picture's height. This ratio is commonly referred to as the picture's aspect ratio. Industry standards and video equipment have developed, over the years, a limited number of aspect ratios in which video is displayed. For example, television receivers employing the NTSC system produce a video picture having a 4:3 aspect ratio. Conversely, digital television (DTV) pictures and typical movie pictures have aspect ratios of 16:9, and have significantly greater width to height ratios than the NTSC system. Digital television and movie pictures are generally referred to as “widescreen” and are considered to provide a more realistic picture since people normally perceive their surroundings with a greater sense of width than height.
Until recently, 16:9 movies, in order to be displayed on television sets, have been reformatted, or “cropped” so that only a center portion of the picture is displayed on the 4:3 television set. This is commonly referred to as “pan and scan” and is problematic in that it results in the loss of large amounts of video data beyond the scanned region. A common alternative to pan and scan is letterboxing. This maintains the 16:9 aspect ratio for the displayed picture and inserts black bars above and below the picture. Unfortunately, this method results in the loss of display “real estate.”
Recently, with the advent of DTV and other forms of digital media such as digital video disks (DVD), television sets have been produced with widescreen 16:9 displays. These widescreen displays can play DTV and other 16:9 signals without loss of video data and without sacrificing display real estate. However, a widescreen 16:9 display provided with a NTSC 4:3 input signal will typically insert black curtains on the sides of the original 4:3 picture.
A problem exists in the field of video production and broadcasting when a video production switcher is presented with input signals having both 4:3 and 16:9 aspect ratios. While it is possible that DTV will result in new video sources and footage being shot in the widescreen 16:9 aspect ratio, broadcasters will still have to deal with a large quantity of archive and file footage. Further, during the DTV phase in period, which is likely to take many years, many video sources will continue to film in standard NTSC 4:3 format. If no conversion between aspect ratios is made, a 4:3 display will squeeze a 16:9 input signal so that the entire picture fits within the smaller display, making the picture skinny. Similarly, a 16:9 display will expand a 4:3 input signal, making the picture look fat. This problem drastically reduces the ability of the broadcaster to successfully mix video signals having different aspect ratios.
Video mixing is typically accomplished via a mixing system, known in the art as a video switcher. The purpose of a switcher is to mix a plurality of sources of video into a single video signal ultimately to be broadcast or recorded as a single image, either still or dynamic. Known switchers create effects such as wipes, dissolves and keys. For example, a switcher can change scenes by “wiping” from one scene to another, or by dissolving one scene into another directly, or via a neutral, e.g., black, background. Additionally, a switcher can mix the output of a character generator, for example, with a background input, thereby “layering” text on top of the background in accordance with a particular key signal, e.g., a self key, luminance key or a preset patternkey. Known switchers can take virtually any input signal and layer that signal on virtually any background.
Generally, a switcher includes at least one and usually multiple multi-level effects (MLE) amplifiers or mixers, each capable of mixing two or more video inputs to create a single video output signal. If it is desired to produce a composite image that includes more signals than a single MLE can accommodate, then the output of one MLE can be fed into the input of a second downstream MLE where further layering can be accomplished. This process can continue until all available MLEs on the switcher are consumed, whereby a highly complicated video image can be devised. Aspect ratio conversion of input video signals is necessary to enable video signals of different aspect ratios to be mixed together.
Prior art solutions to this problem have included the use of an external aspect ratio converter (ARC) to manipulate an incoming video signal from either 16:9 to 4:3 or from 4:3 to 16:9. The ARC is typically connected to a video switcher input to provide an aspect ratio converter input. The output input must also be provided directly to the switcher. The ARC must be fed by a switcher auxiliary bus. Although operative for converting the aspect ratio of an input signal, this system tends to be relatively complex and difficult to set up. Further, a separate auxiliary bus is necessary to exploit the functionality of an ARC. Thus, multiple additional cables and connectors are required to set up the proper connections between the video switcher and external ARC. Moreover, in operation, a switcher operator must initiate the use of the external ARC by depressing buttons to access the auxiliary bus and properly route the desired video signal through the ARC and back into the switcher. If the switcher operator wants to use the original video signal, this signal must be manually chosen on the switcher. In modern, fast-paced, real time video production, however, these additional set up requirements and elaborate operator controls are highly undesirable.
Additionally, control of an ARC in the prior art typically resides with the ARC itself, not with a control panel of a switcher. Accordingly, ARC implemented conversions must be set up in the ARC beforehand, as it is difficult to reprogram an ARC and control a switcher at the same time. This again hampers a switcher operator from fast-paced video editing since only effects previously arranged or programmed can be implemented.